Overall Aims 1. To define the fundamental cognitive deficits in patients with schizophrenia, using principles adapted from cognitive and experimental neuropsychology. 2. To examine the neural circuit hypotheses of schizophrenia by investigating cognition in other conditions with known neural mechanisms that can serve as "Model syndromes" such as Huntington's disease or patients with circumscribed lesions. 3. To study the relationships between disordered cognition and psychopathology using patients with mood disorders and/or with psychotic disorders. 4. To develop and apply new cognitive tasks to patients with schizophrenia, emphasizing tests found to be sensitive to brain areas considered abnormal (according to imaging and/or animal studies) in schizophrenia.